Gmail · MIME preflight · local
Count the bytes Gmail actually carries.
Choose attachments and compare their estimated base64 MIME size with Gmail’s 25 MB personal limit or your own administrator-set limit. File contents are never opened or uploaded.
How to check attachments against Gmail's limit
- Choose the files you plan to attach.
- Pick Personal Gmail, with its 25 MB limit, or enter a custom limit that your administrator has set.
- Read the total estimated size of the message and whether it is under the limit.
Why the size is larger than the files
Email carries binary attachments as base64 text, and every three bytes of file become four characters. The checker applies that expansion to each file, rounding to complete four-character blocks, and adds the results. A set of attachments that totals 19 MB on disk can therefore exceed 25 MB in the message. Headers, boundaries, line wrapping and the body text add a little more, so a result close to the limit is a warning, not a guarantee that the message will go through.
If your files are too large, compress images and PDFs with the tools on this site, or share a link to a cloud-stored file instead of attaching it. Remember that recipients' mail systems can have their own, lower limits.
Files are not opened
The checker runs in your browser, inside an isolated frame on this page that has no network access. Your file is read and written back by your own device, so it is not uploaded to TNAADO or anyone else, and nothing is stored. The advertising on this page sits outside the frame and cannot see what you choose. Only the names and byte sizes reported by your browser are used. The contents of your files are never read.
- Sizes are decimal megabytes: 1 MB is 1,000,000 bytes.
- Workspace administrators can set different limits.
Why the MIME number is larger
Email commonly carries binary attachments as base64 text. Each three source bytes become four base64 characters, rounded to a complete four-character block. This checker uses 4 × ceil(bytes / 3) for every selected file, then compares the sum with the limit you chose.
Message headers, MIME boundaries, line wrapping and body text add more bytes, so a result close to the limit is a warning rather than a delivery guarantee. Gmail says personal accounts can attach up to 25 MB and replaces larger totals with a Google Drive link.
Official sources checked 15 October 2026: Gmail attachment limits and RFC 2045 base64 MIME encoding.
Frequently asked questions
Why can a total under 25 MB still be risky?
The encoded files are only part of the message. Headers, boundaries, line breaks and the message body also use space, and administrator or receiving-server limits can differ.
Are the selected attachments uploaded?
No. The page reads only each file’s name and byte size from the browser. It does not open, store or send the file.
Estimate, not a send test
This page does not connect to Gmail and cannot test recipient-server policies or blocked file types.